Rechargeable batteries manufactured from laminates of solid polymer electrolytes and sheet-like anodes and cathodes displays many advantages over conventional liquid electrolytes batteries. These advantages include lower overall battery weight, high power density, high specific energy, longer service life, and environmental friendliness since the danger of spilling toxic liquid into the environment is eliminated.
Lithium polymer battery components include positive electrodes, negative electrodes and an electrolyte separator capable of permitting ionic conductivity, such as an electrolyte consisting of a polymer and a lithium salt, sandwiched between the positive and negative electrodes. The negative electrodes, or anodes, are usually made of light-weight metals such as alkali metals and alloys, typically lithium metal, lithium oxide, lithium-aluminum alloys and the like, or of carboneous material such as coke or graphite intercalated with lithium ion to form LixC. The composite positive electrodes, or cathodes, are usually formed of a mixture of insertion material, electronic conductive filler, usually carbon or graphite or mixture thereof, and an ionically conductive polymer electrolyte material, the mixture being set on a current collector, for example, a thin sheet of aluminum.
Composite cathode thin films are usually obtained by solvent coating onto a current collector or by melt extrusion deposited onto the current collector film.
Similarly, the polymer electrolyte separator layer is typically produced by solvent coating or by melt extrusion. Solid lithium polymer electrochemical cells are typically manufactured by separately preparing the positive electrode, the electrolyte separator and the negative electrode and thereafter laminating each component together to form an electrochemical cell. U.S. Pat. No. 5,536,278 to Armand et al. discloses one method of assembling the various components of a solid lithium polymer electrochemical cell. The positive electrode thin film is coated or layered onto a current collector. The polymer electrolyte is coated onto a plastic substrate such as a film of polypropylene. The positive electrode is thereafter laminated onto one face of the electrolyte, and the plastic substrate is then removed from the other face of the electrolyte and the lithium negative electrode is applied thereon. Although this manufacturing process is reasonably efficient for research and development and small-scale production of lithium polymer electrochemical cells, it is inadequate for large-scale production of such cells.
U.S. Pat. No. 5,100,746 to Gauthier discloses a method of laminating simultaneously a plurality of layers of components of an electrochemical cell that is adapted to speed up the manufacturing process, wherein double-layer solid polymer electrolyte/composite positive electrode sub-assemblies are subsequently associated with the other constituent layers of the electrochemical cell.
Co-pending U.S. Patent Application Publication no. 2003/0215710A1 discloses an efficient method of manufacturing a positive electrode film through a single or twin screw extruder and either depositing the positive electrode film directly onto a moving current collector film, or handling the positive electrode film through one or more rollers and thereafter laminating it onto a moving current collector film. To achieve cost-effective production levels and to produce a high quality electrochemical cell, the lamination of the positive electrode film onto the current collector must be fast and the positive electrode film must adhere properly onto a substrate such as a current collector.
In order to improve the efficiency of the production process for large-scale manufacturing of lithium polymer batteries, there is a need for an improved method and apparatus for laminating a composite positive electrode onto a substrate support film.